| Title | Tuning the coupling of an individual magnetic impurity to a superconductor: quantum phase transition and transport |
| Authors | Laetitia Farinacci, Gelavizh Ahmadi, Gael Reecht, Michael Ruby, Nils Bogdanoff, Olof Peters, Benjamin W. Heinrich, Felix von Oppen, Katharina J. Franke |
| Journal | Physical Review Letters |
| Vol. 121, 2018, pg. 196803 |
| Abstract | The exchange scattering at magnetic adsorbates on superconductors gives rise to Yu-Shiba-Rusinov (YSR) bound states. Depending on the strength of the exchange coupling, the magnetic moment perturbs the Cooper pair condensate only weakly, resulting in a free-spin ground state, or binds a quasiparticle in its vicinity, leading to a (partially) screened spin state. Here, we use the flexibility of Fe-porphin molecules adsorbed on a Pb(111) surface to reversibly and continuously tune between these distinct ground states. We find that the FeP moment is screened in the pristine adsorption state. Approaching the tip of a scanning tunneling microscope, we exert a sufficiently strong attractive force to tune the molecule through the quantum phase transition into the free-spin state. We ascertain and characterize the transition by investigating the transport processes as function of tip-molecule distance, exciting the YSR states by single-electron tunneling as well as (multiple) Andreev reflections. |
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